JP2533203B2 - Video signal processing method - Google Patents

Description

The present invention relates to a video signal processing method.

(Prior Art) Video signal (electrical signal) output from a TV camera, etc.
Is finally converted into an optical signal by a cathode ray tube monitor or the like, and the subject image is displayed by the brightness of light.

At this time, the light Lo generated on the cathode ray tube and the electric signal Eo input to the cathode ray tube have a non-linear relationship, and have the relationship shown in the equation (1). (Fig. 6 is its characteristic diagram) Lo = K1 · Eo ^{1 / 0.45} ……… (1) (K1 is a constant) On the other hand, the input light Li at the camera side image sensor and the electrical signal Ei generated by it are linear. , And the relationship shown in equation (2). (Fig. 4 is its characteristic diagram) Ei ＝ K2 ・ Li ……… (2) (K2 is a constant) Then, in order to correct the non-linear characteristic in the cathode ray tube,
On the camera side, the gamma process shown in equation (3) is normally performed.
(Fig. 5 is the characteristic diagram) Eo = K3 · Ei ^0.45 (3) (K3 is a constant) By the way, considering the noise mixed in during the transmission of the video signal, the video signal level is small. The noise mixed in the vicinity of the black level has a characteristic of being more easily perceived by human eyes than the noise mixed in the vicinity of the white level having a large signal level (even when the noise of the same amplitude is mixed). Therefore, it is advantageous to gamma-process the video signal output from the image pickup device of the camera as much as possible in the preceding stage.

Further, when the video signal from the image pickup device of the camera is digitally converted, if it is quantized with the same number of bits, it is better to quantize the gamma-processed signal Eo as shown in FIG. Compared to quantization, the actual signal is compressed, and the brightness that can be expressed in the range of "e" shown in FIG. 7 is expanded (the dynamic range is expanded).
The ability of the D converter can be effectively utilized.

As described above, it is effective to perform gamma processing in the front stage as much as possible in order to prevent noise and to digitize a video signal.

However, in the matrix circuit that corrects the hue of the video signal, each signal of the red channel (Rch), the green channel (Gch) and the blue channel (Bch) is added or subtracted from the signal of the channel itself.

For example, in Rch, the processing of Rm = K4 (R−G) + K5 (R−B) (4) (K4 and K5 are constants) is performed. Causes a problem that it cannot be added or subtracted as it is.

Here, the conventional technique will be described with reference to FIGS. 2 and 3.

First, the case of FIG. 2 in which all the circuits are configured in an analog system will be described.

The output of the Rch image pickup device 1 is input to the Rch preamplifier 4, and the Rch video signal ERa is obtained. Similarly, Gch and Bch are also input to dedicated preamplifiers 5 and 6, respectively, and Gch video signal EGa and
Obtain the Bch video signal EBa.

Then, these Rch video signals ERa, Gch video signals EGa, Bc
Each of the h video signals EBa has a linear relationship with the brightness and is directly input to the analog matrix circuit 7,
The hue is corrected by the matrix constant set here.

Next, the Rch video signal ER output from the matrix circuit 7
Ma is gamma-processed by the Rch analog gamma processing circuit 8 to obtain an Rch video signal E′RMa.

Gch and Bch are processed in the same manner as Rch, and a Gch video signal E′GMa and a Bch video signal E′BMa are obtained.

An example in which the all-analog circuit shown in FIG. 2 is digitized will be described with reference to FIG.

In FIG. 3, Rch image sensor 1, Gch image sensor 2 and Bc
The image pickup device 3 for h, the preamplifier 4 for Rch, the preamplifier 5 for Bch and the preamplifier 6 for Bch are the same as in FIG. 2, but the hue of the Rch video signal ERa, Gch video signal EGa and Bch video signal EBa is adjusted. Before doing so, Rch analog gamma processing circuit 8, Gch analog gamma processing circuit 9 and Bch
Are input to the analog type gamma processing circuit 10 for gamma processing. Then, the gamma-processed Rch video signal E'Ra is input to the Rch A / D converter 11, where it is converted from an analog signal to a digital signal. Similarly, Gch and Bch are also A / D converted by the Gch A / D converter 12 and the Bch A / D converter 13. Then, the digitally converted Rch video signal E′Rd, Gc
The h video signal E'Gd and the Bch video signal E'Bd are then input to the digital matrix circuit 14, and the hue is corrected by the matrix constant set here.

(Problems to be Solved by the Invention) In the above-mentioned conventional technology, when digitizing a video signal,
Since the signal processing procedure is gamma processing, analog-to-digital conversion, and matrix processing (hue adjustment), the image signal subjected to matrix processing becomes non-linear with respect to brightness. Therefore, there is a problem in that the addition and subtraction in the matrix processing of the Rch, Bch, and Gch signals cannot be processed correctly, and ideal hue correction cannot be performed.

In order to solve these drawbacks, the present invention aims at performing ideal hue correction by digitizing the signal processing and performing matrix processing (hue correction) on the signal portion that is linear with respect to the brightness. Is.

(Means for Solving the Problems) In order to achieve the above object, the present invention implements a video signal processing procedure by gamma processing, converting an analog video signal into a digital video signal, and degamma processing (inverse function processing of gamma processing). The matrix processing (hue correction) and the gamma processing are performed in this order, and a degamma processing means is inserted into the matrix processing unit so that a digital signal and a signal linear to the brightness can be input.

(Function) As a result, after gamma processing, the analog video signal is converted to a digital video signal, so the performance of the A / D converter can be effectively utilized, and matrix processing (hue correction) is performed.
In R, since the Rch, Bch, and Gch video signals that are linear with respect to brightness can be added or subtracted, they are mixed with other channels regardless of whether the video signal level is low (around the black level) or high (around the white level). Since the signal ratio is constant,
The hue can be kept constant without being affected by the video signal level.

(Embodiment) An embodiment of the present invention will be described with reference to FIG.

The respective outputs converted into electric signals by the Rch image pickup device 1, the Gch image pickup device 2, and the Bch image pickup device 3 are input to the Rch preamplifier 4, the Gch preamplifier 5, and the Bch preamplifier 6, and are amplified. Rch production signal ERa, Gch video signal EGa,
Obtain the Bch video signal EBa.

Next, the Rch video signal ERa, the Gch video signal EGa, and the Bch video signal EBa are input to the Rch analog gamma processing circuit 8, the Gch analog gamma processing circuit 9, and the Bch analog gamma processing circuit 10, respectively. After being processed, Rch video signal E'Ra, Gch video signal E'Ga and Bch video signal E'Ba are obtained.

In order to digitize these gamma-processed video signals, the Rch video signal E'Ra, Gch video signal E'Ga, and Bch video signal E'Ba are Rch A / D converter 11 and Gch A / D converter. The signals are input to the converter 12 and the Bch A / D converter 13, and become the Rch video signal E′Rd, the Gch video signal E′Gd and the Bch video signal E′Bd.

Here, these Rch video signals E′Rd and Gch video signals E′G
Since the d and Bch video signals E'Bd are gamma-processed, the hue cannot be directly corrected as it is.

Therefore, before correcting the hue, these signals are converted to Rch.
Degamma processing circuit 17, Gch degamma processing circuit 18 and Bc
It is input to the degamma processing circuit 19 for h, and the non-linear gamma-processed video signal is returned to linear. After that, it is input to the digital matrix circuit 14 and the hue is adjusted by the matrix constant set here.

The output of the digital matrix circuit 14 is input to the Rch digital gamma processing circuit 20, the Gch digital gamma processing circuit 21, and the Bch digital gamma processing circuit 22, where it is gamma-processed and ideally Corrected Rch video signal E'RMd, Gch video signal E'GMd and B
The ch video signal E'BMd is obtained.

(Effect of the Invention) According to the present invention, since the video signal is gamma-processed and then digitized, the ability of the A / D converter can be effectively utilized, and the hue adjustment can be performed linearly. It can be done in the state of. Therefore, compared with the analog type, the number of degamma processing means increases, but since the video signal can be processed as a digital signal, it has excellent frequency characteristics and phase characteristics, and Rch, Gch,
It is possible to realize a video signal processing method with very little variation in characteristics between B channels.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention, FIG.
FIG. 3 is a block diagram showing the overall configuration of the prior art, FIG. 4 is an input / output characteristic diagram of an image sensor, FIG. 5 is a gamma processing characteristic diagram, FIG. 6 is a cathode ray tube input / output characteristic diagram, and FIG. It is a luminance dynamic range comparison characteristic diagram before and behind a gamma process. 8: Rch analog gamma processing circuit, 9: Gch analog gamma processing circuit, 10: Bch analog gamma processing circuit, 1
1: Rch A / D converter, 12: Gch A / D converter, 13: Bch A / D converter, 14: Digital matrix circuit, 17: Rch degamma processing circuit, 18: Gch degamma Processing circuit, 19: Bch degamma processing circuit, 20: Rch digital gamma processing circuit, 21: Gch digital gamma processing circuit, 22: Bch digital gamma processing circuit.

Claims (1)

(57) [Claims] 1. When processing a video signal, first, the analog video signal is subjected to non-linear processing, the non-linear analog video signal is converted into a digital signal, the non-linearly processed digital signal is returned to a linear digital signal, and then the A video signal processing method, wherein hue correction processing is performed in the state of a linear digital signal.